A new catalyst system for the Pd-catalyzed cross-coupling of organozinc reagents with aryl halides (Negishi coupling) has been developed. This system permits efficient preparation of hindered biaryls (tri- and tetra-ortho-substituted), functions effectively at low levels of catalyst, and tolerates a wide range of functional groups and heterocyclic substrates. A systematic study of ligand structure was performed and was correlated with catalyst activity.